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I do a lot of restoration and second life rebuilds on riding mowers. The older B&S engines, say pre- 2004, usually recommend using 30wt. oil. It seems later model
engines suggest using synthetic 10w-30 oils. These mower live and do most of their work in 90+ degree weather.

Is it due to the retarded timing for emissions compliant certification? Question is: Can I use the multi-viscosity synthetic oil in current B&S engines? Opinions?

Several of the reasons behind the older engines running 30w oil was they had sloppy tolerances, and multi grade oils are too thin for those engines. And the older oils were not as good of quality of more advances oils. Briggs is supplying their own 5w30 and 15w50 synthetic oils and Kohler for the most part has discontinued their 10w30 and are now subbing the newer 10w40 synthetic to their dealers when they order oil from their parts distributor.

ILENGINE said:

Several of the reasons behind the older engines running 30w oil was they had sloppy tolerances,

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Alot of stuff i own are 80's ish, a few 70's. I use at lease 10w40. It being thicker helps alot to minimize alot of the rattling.

upupandaway said:

Alot of stuff i own are 80's ish, a few 70's. I use at lease 10w40. It being thicker helps alot to minimize alot of the rattling.

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Nothing like correct
the multi grade & the mono grades are exactly the same viscosity at operating temperature.
The difference is the viscosity when cold
The 30 is 30 when cold while the 10W 30 is 10 when cold.
So in lawnmowers all the multigrade will do is tend to leak from anywhere it can when the mower is not in use.

Because 30W at room temperature is fairly thick & slow flowing the oil holes have to be big.
The problem with this is at operating temperature when the oil is thin, the holes are too big so the engine over lubes.
This is one reason why old engines run forever but tend to carbon encrust the piston top & head .

An engine designed for multigrade oils will have oil galleries that are the right size for the oil at operating temperature because at room temperature it is a lot thinner and can get through the smaller spaces in sufficient quantities to keep the engine lubed.

Also with multigrades being thinner at room temperature they have less viscious friction so the engine turns over easier so t is easier to start.
To put a mower perspective on it , Honda was one of the first engines to run multigrade oils
Hondas are easier to start than a Briggs because of the thinner oil at cranking temperatures.
When my little old ladies & men are having trouble starting their old engines I switch them to 10W 40 and they think I am some sort of magician.

Now the only problem is most multigrades are detergent so they hold all of the crud from the engine in fine suspension to allow for easy filtering which is fine if your mower has a filter . However most of the old mowers do not have filters so if you put multigrade in them you really need to change the oil every season because the crd will not fall to the bottom and make a stable sludge thus stop circulating in the engine.

Thanks for your input!

I have decided not to overthink oil in OPE. Stens 30wt. In all the push mowers except hondas. All riders and Honda push mowers get Stens 10w30. Both have zddp additive packages. I go through about 50 gallons or so of oil a year in the shop. No oil issues so far. No expensive synthetics. No "best brand name" oils. No miracle additives. You would have thought i would have blown at least a few up just using regular old oil. ? i do run 15w40 in my 45 year old LoBoy tractor. She has a lot of hours on her.

All modern engine oils not intended for racing or specifically say non-detergent are detergent oils. They stop sludging by suspending particulates in the oil. Change the oil often in that push mower!

Most engine wear occurs in those first moments after starting, during what we call "warm-up". Multi-grades come into their own in water-cooled engines and air-cooled engines that have a tremendous oil supply. This is simply due to the slower or "extended" warm-up times in those engines.

In your traditional small, single-cylinder mower engine, the warm up time is probably under 1 minute. In such cases, I wouldn't say multi-grades are required, especially if they can be run at a moderate warm-up speed during those first 30 seconds. But in a modern mower that runs at a fixed RPM, the engine is required to go from cold start to full working RPM in a matter of seconds, and a multi-grade that starts to lubricate instantly is at a slight advantage.

Born2Mow said:

\
\ But in a modern mower that runs at a fixed RPM, the engine is required to go from cold start to full working RPM in a matter of seconds, and a multi-grade that starts to lubricate instantly is at a slight advantage.

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One thing i do, i have no idea if it helps, on my push mower, i always pull the plug wire off, and pull the rope several times with the idea of getting the oil splashed around before it starts. No idea if it helps, just makes me feel better i guess.

bertsmobile1 said:

Nothing like correct
the multi grade & the mono grades are exactly the same viscosity at operating temperature.
The difference is the viscosity when cold
The 30 is 30 when cold while the 10W 30 is 10 when cold.

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So what is not correct? I use 40. I said nothing about how my oil compares to straight 40 or 10w30 weight oil
40weight oil is thicker than 30 when hot and my stuff rattle less because of it.
Last time i checked I cut my grass longer than 1 minute so cold viscosity is a moot point.
I change my oil yearly anyway so another moot point.

upupandaway said:

So what is not correct? I use 10W40. I said nothing about how my oil compares to straight 40 or 10w30 weight oil

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No fight here. If I restored older engines, I'd be using 10W40 or 15W40 diesel oil too. Maybe even 20W50 !!

40 weight oil is thicker than 30 when hot and my stuff rattle less because of it.

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And you said most of your engines are used in 90° temps. They will be harder to pull start. But if given 15-30 seconds of idling to warm up they'll be fine.

Last time i checked I cut my grass longer than 1 minute so cold viscosity is a moot point.

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Cold viscosity is not a moot point, it's one of many considerations. And yes, it's ranking is way on down the list, but that hardly makes it moot. As already pointed out, cranking will be harder. Pull cords may wear out faster. And on top of that the "40" won't really start to lubricate for several minutes. Luckily you'll be covered by the 10 in the 10W40.

Many people believe that just because the metal of the piston and cylinder get hot that they are "good to go". It's not the metal that has trouble warming to temp... it's the oil that needs to come up to temp. Oil most definitely has a preferred operating temp range, both for the ambient air temp AND the engine operating temp. A look at your car owner's manual will usually produce a nice little chart to show this... because the oil you use in Boston is not the preferred oil for Death Valley.

I change my oil yearly anyway so another moot point.

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I agree, for a walk-behind that's more than enough. You're probably not getting more than 40 hours during a mowing season. Just be sure to change it right after you mow the lawn, while the oil is HOT ! The difference in the newer oils (versus those you may have grown up using) is that all the trash is suspended in the oil due the detergents. To get that trash out of the engine you'll want to empty the oil while all the bad stuff is in suspension.

I personally find tipping the whole mower to be much more efficient way than using the old drain plug.

Hope this helps.